The present invention relates to a d.c. voltage monitor and in particular to a circuit for detecting voltage drops during power interruptions and start-up.
In certain applications wherein a D.C. supply voltage is utilized as a power supply, it is critical that the supply voltage not fall below a selected threshold. For example, in some microprocessor application it is desirable to have the power supply inhibited during any fall off from a preselected level rather than have the sensitive circuitry powered at an insufficient voltage level.
Heretofore, such critical voltages were commonly monitored by comparison to a fixed reference. When the voltage fell below the reference value a reset pulse was generated. The principal problem with such systems is that their sensitivity range is limited.
In view of the above, it is the principal object of the present invention to provide a D.C. supply voltage monitor circuit which does not rely on any fixed reference but rather uses a selectable reference which may be varied to provide a wide range of monitor sensitivity as required by the particular application.
A further object is to provide such a circuit which is relatively insensitive to set up tolerances.
Still another object is to provide such a circuit which may be assembled utilizing conventional and relatively inexpensive components.
Still other objects will be apparent from the following description.